Adhesive compositions are used for a variety of purposes in the fabrication and assembly of semiconductor packages and microelectronic devices. The more prominent uses include bonding of electronic elements such as integrated circuit chips to lead frames or other substrates, and bonding of circuit packages or assemblies to printed wire boards. Adhesives useful for electronic packaging applications typically exhibit properties such as good mechanical strength, curing properties that do not affect the component or the carrier, and rheological properties compatible with application to microelectronic and semiconductor components.
Due to the ever-increasing pressure to reduce the size of semiconductor packages, there has been a recent interest in thin die, and the use of these thin die in stacked packages (i.e., at least one die stacked on top of another). These types of assemblies conserve circuit board real estate without sacrificing overall performance of a device containing such an assembly. However, the use of thin die has created challenges for the semiconductor packaging industry.
Semiconductor packaging using conventional die attach paste involves lowering a die onto a dispensed pattern of die attach paste until a fillet is formed around the die edges. Standard die attach techniques can sometimes limit the use of paste in tight tolerance packages, where the distance between fillet and bond pads on a substrate are minimal. In addition, for thin die packages conventional die attach paste tends to form bulky fillets that overflow onto the top of the die, thereby contaminating the top of the die. As a result, package assemblers of thinner die have had to use die-bonding film, which increases material cost and incurs capital equipment investment.
Moreover, when using conventional semiconductor packaging techniques, after the die is lowered onto a dispensed pattern of die attach paste, the die is typically pressed onto the paste to ensure proper bonding to a substrate. This step in the die attach process has become problematic as semiconductor die have become increasingly thin, i.e., pressure applied to thin die can crack the die. Packages containing cracked die must be scrapped, and the risk of rejected packages is multiplied when stacked die packages are assembled.